Heading to the gym after work? You probably will leave that stuff in your car.

Savvy thieves know this.

A rash of car burglaries is infecting parts of eastern Hillsborough County, with the thefts concentrated in parking lots of gymnasiums and parks and at day-care centers and shopping centers. The common denominator is the locations mostly are places where people go in, don’t spend more than an hour, and leave.

Hillsborough County sheriff’s deputies say thieves target vehicles in the parking lots of those types of businesses, usually targeting vehicles where expensive items are in plain sight.

Here’s what deputies say the burglars do: They walk the lot, looking inside the cars for valuables. Deputies say many times, the doors are unlocked and entry is gained by just opening the door.

If the doors are locked, the thieves smash a window, reach in and steal the stuff.

Catching these thieves is difficult, said sheriff’s Sgt. Steve Lewis, who said since Jan. 1, there were about 800 reported car break-ins in the unincorporated parts of the county. Each of the sheriff’s four districts has averaged about 200 car burglaries since the first of the year, he said.

“It’s tough,” he said. “If they break a window, reach in and grab a purse and go, they don’t leave much evidence behind.”

Sometimes, arrests can be made if the culprits touch the hood or window of the car and leave fingerprints or if DNA evidence is left behind. Or if someone sees them and gets a tag number. Or if there is video surveillance video available.

Lewis urged people to hide valuables under seats to keep them out of sight from the outside, or take the items in with them.

“It’s crazy,” Lewis said on Friday. “We had three cases just yesterday.”

Lewis said a woman who went to the YMCA on Kingsway Road in Brandon did the right thing by putting her purse in the trunk. Unfortunately, that time it didn’t protect her, he said.

“She parked near the entrance and within five minutes her car alarm went off,” he said. The thief likely saw her put her purse in the trunk. He broke the window, popped the trunk and made off with the purse and its contents. Within a day, he said, her credit card had been used.

People going to the gym or a quick jog in the park are only going to be gone for a short period of time, he said, often thinking their belongings are safe in their cars.

Motivation for thieves might be to steal identities, or just to grab valuables they can sell on the street.

Joe Mangione, vice president of risk management for the YMCA in the Tampa area, said members get plenty of warning about vehicle burglaries.

“We post signs in our parking lot,” he said. One YMCA had a rash of burglaries, he said, and video surveillance cameras were put up. “We haven’t had a problem there since.’’

He has noticed that car burglaries seem to come in waves.

“A lot of it is seasonal,” he said. “It increases in the summertime; it might have something to do with kids being out of school.

“It happens from time to time; there isn’t one location where it’s a problem,” Mangione said. “It really doesn’t matter where you are; you could be at the mall, Publix or Target or Lowe’s. (Thieves) do like large parking lots, though.”

The theft of wallets and purses from vehicles parked in businesses spiked five years ago, when deputies warned the public about a “felony lane” gang of thieves from South Florida that was targeting Tampa.

The gang broke into cars and stole identification, credit cards and checkbooks and immediately went to the drive-through lanes of banks to cash checks or do other cash transfers.

In 2009, deputies said, the gang had stolen about $50,000 from banks by stealing the identities of their patrons.

Lewis said investigators are unsure if the car burglaries occurring since the first of the year are connected to any “felony lane” ring.

Inside the city of Tampa, the break-ins of cars at gyms and parks and stores never lets up.

“It has been going on for years,” said Tampa police spokeswoman Andrea Davis. “Criminals know that people going inside to work out don’t want to bring all of their stuff in.

“Unfortunately it isn’t new,” she said, “but it’s very frustrating for law enforcement.’’